The present invention relates to a solar cell device having at least one solar cell module designed to supply a consumer.
If solar cells are to be used for supplying electric consumers it is necessary as a rule to connect a plurality of solar cells one with the other. Normally, individual solar cells and/or solar cell modules are connected in parallel or in series. In the case of those types of connection shading of individual cells or modules may lead to heavy losses with respect to short-circuit current, no-load voltage and power output. In order to avoid such losses, one normally makes use of connection variants using bypass diodes or coupling diodes.
In principle, if output voltage values higher than those of a single cell and/or a single module are to be obtained, two options are available.
According to a first variant, a number of identical individual cells and/or modules, being as similar as possible, are connected in series to obtain an output voltage equal to an integer multiple of the voltage of a single cell or a single module, the connection being effected especially by monolithic integrated series connection, as is usual for thin-film modules.
Alternatively, it is possible to provide for voltage conversion via energy transformation. In that case, an inductance is employed to store the energy supplied to it via a switching transistor, and to release it later. Depending on the timing of such release of energy, the arrangement so realized is a forward converter or a flyback converter.
If an output voltage not higher than that of the individual cells or of the modules is desired, the cells or modules are connected in parallel.
Series connection of individual solar cells or modules is connected with the disadvantage that the maximum current is determined by the least efficient cell. The least efficient cell is that cell which supplies the least current under given illumination conditions.
When connecting solar cells using the monolithic series connection system undesirable resistances parallel to the individual cell will be produced. In addition, due to differences in illumination, the maximum power output of the connected cells and/or modules will be smaller than or maximally equal to the power output of the weakest cell. Especially when solar cells or solar modules are integrated in garments, for example, for mobile use the different individual cells or modules cannot possibly be illuminated identically. Considering that the input power of the individual cells or modules is very low, the illumination being very poor in most of the cases, such shading losses are extremely problematic. On the other hand, when the cells and/or modules are connected in parallel, compensating currents will be produced between individual cells or modules. Such currents have the effect to adapt the individual voltages because all the individual cells and/or modules necessarily must have the same potential in a parallel connection.